Probably not “angry” downvotes. OP provided a link where it’s explained exactly why the switch was made. Even if you don’t care for Rust it’s pretty clear that this was done with more purpose than just “Ooo let’s make it in Rust for fun”

Florisboard is the keyboard app that stopped me jumping between keyboard apps

Docs can only really help you if your problem is “I have used X from the library Y, yet I do not understand the baseline definition of X sufficiently and this is causing issues”. A lot of problems in practice are much more fundamental than that